EVIDENCE FOR DELOCALIZATION IN HIGH-PURITY N-TYPE INP

Low temperature Hall data on several low compensated, high purity n-type epilayers are reported. Deep donor centres present in the samples are neutral in the temperature range under consideration, and conduction is examined in a band of shallow donor impurities. Mott variable-range hopping is observed for majority impurity concentrations above 1.3 x 10(15) cm-3. For more lightly doped and less compensated samples, unusually high impurity conduction is consistently observed. which is well described by a conductivity of the form sigma = alpha0 + bT1/2, a signature of interaction effects in barely metallic samples. This Anderson-like transition to electronic delocalization is plausible, if there is correlation in the spatial distribution of the residual charged donor impurity sites.